Stent mandrel fixture and method for selectively coating surfaces of a stent

ABSTRACT

A stent mandrel fixture for supporting a stent during the application of a coating substance is provided. A method supporting a stent during the application of a coating substance is also provided.

This is a continuation application of U.S. Ser. No. 10/676,545, (nowU.S. Pat. No. 7,198,675), which was filed on Sep. 30, 2003, which isincorporated herein by reference.

TECHNICAL FIELD

This invention relates generally to stent mandrel fixtures, and moreparticularly, but not exclusively, provides a stent mandrel fixture andmethod for coating an outer surface of a stent.

BACKGROUND

Blood vessel occlusions are commonly treated by mechanically enhancingblood flow in the affected vessels, such as by employing a stent. Stentsact as scaffoldings, functioning to physically hold open and, ifdesired, to expand the wall of affected vessels. Typically stents arecapable of being compressed, so that they can be inserted through smalllumens via catheters, and then expanded to a larger diameter once theyare at the desired location. Examples in the patent literaturedisclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S.Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062issued to Wiktor.

FIG. 1 illustrates a conventional stent 10 formed from a plurality ofstruts 12. The plurality of struts 12 are radially expandable andinterconnected by connecting elements 14 that are disposed betweenadjacent struts 12, leaving lateral openings or gaps 16 between adjacentstruts 12. The struts 12 and the connecting elements 14 define a tubularstent body having an outer, tissue-contacting surface and an innersurface.

Stents are used not only for mechanical intervention but also asvehicles for providing biological therapy. Biological therapy can beachieved by medicating the stents. Medicated stents provide for thelocal administration of a therapeutic substance at the diseased site.Local delivery of a therapeutic substance is a preferred method oftreatment because the substance is concentrated at a specific site andthus smaller total levels of medication can be administered incomparison to systemic dosages that often produce adverse or even toxicside effects for the patient.

One method of medicating a stent involves the use of a polyinmericcarrier coated onto the surface of the stent. A composition including asolvent, a polymer dissolved in the solvent, and a therapeutic substancedispersed in the blend is applied to the stent by immersing the stent inthe composition or-by spraying the composition onto the stent. Thesolvent is allowed to evaporate, leaving on the stent strut surfaces acoating of the polymer and the therapeutic substance impregnated in thepolymer.

A shortcoming of the above-described method of medicating a stent isthat both the inner surface and an outer surface of the stent are coatedwith the same therapeutic substance. Accordingly, the therapeuticsubstance will be dispensed locally by being absorbed by the vessel wallfrom the outer surface of the stent and will be dispensed downstream asblood carries the therapeutic substance from the inner surface. In somecircumstances there may be a need of only having the outer surface ofthe stent coated with the therapeutic substance. Alternatively, theremay be a need of coating the outer surface of the stent with a firsttype of a drug and the inner surface with a second type of a drug. Forexample, the stent's outer surface could be coated with ananti-inflamatory drug or anti-restenosis drug to treat inflammation orhyper-migration and proliferation of vascular smooth muscle cells,respectively. The stent's inner wall could be coating with ananti-coagulant to reduce platelet aggregation, clotting and thrombusformation.

Accordingly, a new stent mandrel fixture and method are needed toovercome this shortcoming.

SUMMARY

In accordance with one embodiment of the invention, a stent mandrelfixture is provided, comprising a masking element configured to beinserted through a bore of a stent, the masking element having anexpanded configuration and a retracted configuration and an expansioncausing mechanism capable of expanding the masking element from theretracted configuration to the expanded configuration to cause themasking element to make contact with and mask an inner surface of thestent.

In accordance with another embodiment of the invention, a fixture tosupport a stent during the application of a coating composition to thestent is provided, comprising a hollow tubular member configured to beinserted into a longitudinal bore of a stent; a rod extending throughthe tubular member; and a mechanism to cause the tubular member toexpand and retract to support the stent during the application of acoating composition to the stent.

In accordance with another embodiment of the invention, a fixture tosupport a stent during the application of a coating composition to thestent is provided, comprising a mandrel base; a rod extending out fromthe mandrel base, the rod configured to be moved in and out of themandrel base; and a support element integrated with the rod, the supportelement having a first position of being engaged with the stent and asecond position of being disengaged from the stent, wherein the movementof the rod in and out of the mandrel base causes the engagement anddisengagement of the support element with the stent. A lever can be usedto drive the rod in and out of the mandrel base.

In accordance with other embodiments of the invention, methods ofcoating a stent with a composition are provided, comprising: positioninga stent on a fixture of the invention; and applying a coatingcomposition to the stent.

In accordance with yet another embodiment, a method of coating a stentwith a composition is provided, comprising inserting a tubular memberinside a longitudinal bore of a stent, the stent comprising strutsseparated by gaps; expanding the tubular member such that the tubularmember at least partially extends through the gaps; and applying acoating composition to the stent.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 illustrates a conventional stent;

FIG. 2A and FIG. 2B illustrate a stent mandrel fixture in accordancewith an embodiment of the invention;

FIG. 3A, FIG. 3B, and FIG. 3C illustrate a stent mandrel fixture inaccordance with another embodiment of the invention;

FIG. 3D illustrates a stent mandrel fixture in accordance with anotherembodiment of the invention;

FIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D illustrate a stent mandrelfixture in accordance with another embodiment of the invention;

FIG. 5A and FIG. 5B illustrate cross sections of a stent mandrel fixtureaccording to an embodiment of the invention;

FIG. 5C illustrates a cross section of a stent strut after coating onthe stent mandrel fixture of FIG. 2, FIG. 3, or FIG. 4;

FIG. 6A illustrates a cross section of a stent mandrel fixture accordingto an embodiment of the invention;

FIG. 6B-6D illustrate cross sections of a stent strut after coating onthe stent mandrel fixture of FIG. 2, FIG. 3, or FIG. 4; and

FIG. 7 illustrates a flowchart of a method of coating a stent using thestent mandrel fixture of FIG. 2, FIG. 3 or FIG. 4.

DETAILED DESCRIPTION

The following description is provided to enable any person havingordinary skill in the art to make and use the invention, and is providedin the context of a particular application and its requirements. Variousmodifications to the embodiments will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other embodiments and applications without departing from thespirit and scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown, but is to be accordedthe widest scope consistent with the principles, features and teachingsdisclosed herein.

FIG. 2A and FIG. 2B illustrate a stent mandrel fixture 20A in accordancewith an embodiment of the invention. The fixture 20A for supporting thestent 10 includes a bladder or expandable or elastic tube 23A, athreaded rod 24, a nut 25, and a lock member 26. The stent mandrelfixture 20A can be coupled to engines (not shown) to provide rotationaland lateral motion to a mounted stent 10 during a coating process.

The threaded rod 24 passes through an inner bore of the tube 23A, lockmember 26, and nut 25. The tube 23A is fixed at one end to the lockmember 26 while the nut is rotationally mounted on the rod 24. In analternative embodiments the lock member 26 can also be rotationallymounted to the rod 24 (and therefore not fixed to the tube 23A) therebyenabling the adjustable positioning of the lock member 26. While thelock member 26 as shown has an outer diameter greater than the outerdiameter of the nut 25, it will be appreciated by one of ordinary skillin the art that the lock member 26 can have an outer diameter less than,substantially equal to, or greater than the outer diameter of the nut25. The outer diameter of the lock member 26 must only be at least equalto the outer diameter of the stent 10 so that the stent 10 does notslide past the lock member 26.

The nut 25 is an expansion causing mechanism. Rotation of the nut 25,such that the nut 25 presses against the tube 23A, causes the tube 23Ato compress in a lateral direction against the lock member 26 whileexpanding radially outwards from the rod 24 as shown in FIG. 2B and FIG.5B. Rotation of the nut 25 away from the tube 23A causes the tube 23A toreturn back to its uncompressed or natural state as shown in FIG. 2A andFIG. 5A.

It will be appreciated by one of ordinary skill in the art that the nut25 can be electrically driven or otherwise tightened without humanintervention in order to automate the process of coating a stent 10,thereby increasing throughput. Additionally, with the use of the nut 25,incremental rotation of the nut 25 can allow for the bladder or tube 23Ato be expanded in an incremental fashion.

The tube 23A can be made of or coated with a non-stick substance, suchas TEFLON. In one embodiment, the tube 23A, when compressed laterally,has a length equal to at least the length of the stent 10, therebyenabling masking of the entire length of the inner diameter of the stent10. In another embodiment, the tube 23A, when compressed laterally, hasa length shorter than the length of the stent 10, thereby supporting thestent 10 with minimal contact with the stent 10. In an unexpanded state(i.e., not compressed laterally), the tube 23A has an outer diametersmaller than the inner diameter of the stent 10 (as positioned on thetube 23A). When the tube 23A expands (i.e., is compressed laterally),the outer diameter of the tube 23A expands to at least the innerdiameter of the stent 10, thereby acting to hold the stent 10 in placeand to mask at least a portion of the inner surface of the stent 10. Themasking of the inner surface of the stent 10 prevents the inner surfacefrom being coated with a composition during a coating process.Accordingly, when the tube 23A is in an expanded state, only the outersurface and sidewalls of the stent 10 are coated with the compositionfrom a spray flow, which is discharged from a nozzle assembly (notshown). In other embodiments of the invention to be discussed furtherbelow in conjunction with FIG. 6A to 6D, the tube 23A can be furtherradially expanded to enable masking of the sidewalls in addition to theinner surface of the stent 10.

During operation of the stent mandrel fixture 20A, a stent 10 is loadedonto the fixture by first removing the nut 25 and then placing the stent10 over the tube 23A when tube 23A is in an uncompressed state, as shownin FIG. 5A. The nut 25 is then loaded onto the rod 24 and tightenedagainst the tube 23A, causing the tube 23A to compress laterally andexpand radially outwards from the rod 24, as shown in FIG. 5B. In oneembodiment of the invention, the tube 23A can expand radially outwardsto substantially mask the inner surface of the stent 10, as shown inFIG. 5B. In another embodiment of the invention, the tube 23A cancomprise a flexible and/or thin material, such as latex, and expandsradially outwards to substantially mask the inner surface of the stent10 as well as the sidewalls of the stent 10, as shown in FIG. 6A. Inother words, the tube 23A is capable of protruding at least partiallythrough the gaps 16 between the stent struts 12 to mask the sidewalls ofthe stent struts 12.

After the tube 23A is expanded radially outwards, a spray nozzle (notshown) sprays a composition onto the stent 10. As the inner diameter ofthe stent 10 is masked, only the sidewalls and outer surface of thestent 10 are coated with a composition. In another embodiment of theinvention, the sidewalls can also be masked and accordingly, only theouter surface of the stent 10 is coated with the composition.

After the coating of the stent 10, the nut 25 is loosened, therebyenabling the tube 23A to return to a non-expanded state and furtherenabling removal of the stent 10 from the stent mandrel fixture 20A. Thestent 10 can then have the inner surface coated via electroplating orspray coating. Without masking the outer surface of the stent 10, bothelectroplating and spray coating may yield some composition onto theouter surface and sidewalls of the stent 10. However, the inner surfacewould be substantially solely coated with a single composition differentfrom the composition used to coat the outer surface of the stent 10.Accordingly, it will be appreciated by one of ordinary skill in the artthat this embodiment enables the coating of the inner surface and theouter surface of the stent 10 with different compositions. For example,the inner surface could be coated with a composition having abio-beneficial therapeutic substance for delivery downstream of thestent 10 (e.g., an anticoagulant, such as heparin, to reduce plateletaggregation, clotting and thrombus formation) while the outer surface ofthe stent 10 could be coating with a composition having a therapeuticsubstance for local delivery to a blood vessel wall (e.g., ananti-inflammatory drug to treat vessel wall inflammation or a drug forthe treatment of restenosis).

The components of the coating substance or composition can include asolvent or a solvent system comprising multiple solvents, a polymer or acombination of polymers, a therapeutic substance or a drug or acombination of drugs. Representative examples of polymers that can beused to coat a stent or medical device include ethylene vinyl alcoholcopolymer (commonly known by the generic name EVOH or by the trade nameEVAL); poly(hydroxyvalerate); poly(L-lactic acid); polycaprolactone;poly(lactide-co-glycolide); poly(glycerol-sebacate);poly(hydroxybutyrate); poly(hydroxybutyrate-co-valerate); polydioxanone;polyorthoester;.polyanhydride; poly(glycolic acid); poly(D,L-lacticacid); poly(glycolic acid-co-trimethylene carbonate); polyphosphoester;polyphosphoester urethane; poly(amino acids); cyanoacrylates;poly(trimethylene carbonate); poly(iminocarbonate); copoly(ether esters)(e.g. PEO/PLA); polyalkylene oxalates; polyphosphazenes; biomolecules,such as fibrin, fibrinogen, cellulose, starch, collagen and hyaluronicacid; polyurethanes; silicones; polyesters; polyolefins; polyisobutyleneand ethylene-alphaolefin copolymers; acrylic polymers and copolymers;vinyl halide polymers and copolymers, such as polyvinyl chloride;polyvinyl ethers, such as polyvinyl methyl ether; polyvinylidenehalides, such as polyvinylidene fluoride and polyvinylidene chloride;polyacrylonitrile; polyvinyl ketones; polyvinyl aromatics, such aspolystyrene; polyvinyl esters, such as polyvinyl acetate; copolymers ofvinyl monomers with each other and olefins, Such as ethylene-methylmethacrylate copolymers, acrylonitrilestyrene copolymers, ABS resins,and ethylene-vinyl acetate copolymers; polyamides, such as Nylon 66 andpolycaprolactam; alkyd resins; polycarbonates; polyoxymethylenes;polyimides; polyethers; epoxy resins; polyurethanes; rayon;rayon-triacetate; cellulose; cellulose acetate; cellulose butyrate;cellulose acetate butyrate; cellophane; cellulose nitrate; cellulosepropionate; cellulose ethers; and carboxymethyl cellulose.

“Solvent” is defined as a liquid substance or composition that iscompatible with the polymer and is capable of dissolving the polymer atthe concentration desired in the composition. Examples of solventsinclude, but are not limited to, dimethylsulfoxide, chloroform, acetone,water (buffered saline), xylene, methanol, ethanol, 1-propanol,tetrahydrofuran, 1-butanone, dimethylformamide, dimethylacetamide,cyclohexanone, ethyl acetate, methylethylketone, propylene glycolmonomethylether, isopropanol, isopropanol admixed with water, N-methylpyrrolidinone, toluene, and mixtures and combinations thereof.

The therapeutic substance or drug can include any substance capable ofexerting a therapeutic or prophylactic effect. Examples of agentsinclude antiproliferative substances such as actinomycin D, orderivatives and analogs thereof (manufactured by Sigma-Aldrich 1001 WestSaint Paul Avenue, Milwaukee, Wis. 53233; or COSMEGEN available fromMerck). Synonyms of actinomycin D include dactinomycin, actinomycin IV,actinomycin I₁, actinomycin X₁, and actinomycin C₁. The active agent canalso fall under the genus of antineoplastic, antiinflammatory,antiplatelet, anticoagulant, antifibrin, antithrombin, antimitotic,antibiotic, antiallergic and antioxidant substances. Examples of suchantineoplastics and/or antimitotics include paclitaxel (e.g. TAXOL® byBristol-Myers Squibb Co., Stamford, Conn.), docetaxel (e.g. Taxotere®,from Aventis S.A., Frankfurt, Germany) methotrexate, azathioprine,vincristine, vinblastine, fluorouracil, doxorubicin hydrochloride (e.g.Adriamycin® from Pharmacia & Upjohn, Peapack N.J.), and mitomycin (e.g.Mutamycin® from Bristol-Myers Squibb Co., Stamford, Conn.). Examples ofsuch antiplatelets, anticoagulants, antifibrin, and antithrombinsinclude sodium heparin, low molecular weight heparins, heparinoids,hirudin, argatroban, forskolin, vapiprost, prostacyclin and prostacyclinanalogues, dextran, D-phe-pro-arg-chloromethylketone (syntheticantitlrombin), dipyridamole, glycoprotein IIb/IIIa platelet membranereceptor antagonist antibody, recombinant hirudin, and thrombininhibitors such as Angiomax™ (Biogen, Inc., Cambridge, Mass.). Examplesof such cytostatic or antiproliferative agents include angiopeptin,angiotensin converting enzyme inhibitors such as captopril (e.g.Capoten® and Capozide® from Bristol-Myers Squibb Co., Stamford, Conn.),cilazapril or lisinopril (e.g. Prinivil® and Prinzide® from Merck & Co.,Inc., Whitehouse Station, N.J.); calcium channel blockers (such asnifedipine), colchicine, fibroblast growth factor (FGF) antagonists,fish oil (omega 3-fatty acid), histamine antagonists, lovastatin (aninhibitor of HMG-CoA reductase, a cholesterol lowering drug, brand nameMevacor® from Merck & Co., Inc., Whitehouse Station, N.J.), monoclonalantibodies (such as those specific for Platelet-Derived Growth Factor(PDGF) receptors), nitroprusside, phosphodiesterase inhibitors,prostaglandin inhibitors, suramin, serotonin blockers, steroids,thioprotease inhibitors, triazolopyrimidine (a PDGF antagonist), andnitric oxide. An example of an antiallergic agent is permirolastpotassium. Other therapeutic substances or agents which may beappropriate include alpha-interferon, genetically engineered epithelialcells, dexamethasone, and rapamycin.

FIG. 3A, FIG. 3B, and FIG. 3C illustrate a stent mandrel fixture 20B inaccordance with another embodiment of the invention. The stent mandrelfixture 20B is substantially similar to the stent mandrel fixture 20Aexcept that the fixture 20B includes a substantially airtight inflatablecylinder or bladder 23B, which acts as a masking element to mask aninner surface of the stent 10 during a coating process, coupled to apump 50 via a tube 52 in place of the tube 23A. As shown in FIG. 3C,which includes a cross section of the cylinder 23B, the cylinder 23Bresembles a tire and comprises an outer diameter 54 and an innerdiameter 56, and sidewalls which bound an interior airtight volume 55.The cylinder 23B includes a bore 57 formed by the inner diameter 56through which the rod 24 travels.

The cylinder 23B can be fixed to the lock member 26 and/or nut 25, whichact to prevent lateral movement of the cylinder 23B and stent 10 duringa coating process. In addition, the lock member 26 and/or the nut 25 arerotationally mounted on the threaded rod 24, thereby enablingincremental positioning of the lock member 26 and the nut 25 with thecylinder 23B there between. In an alternative embodiment, the cylinder23B is fixed to either the lock member 26 and/or the nut 25 and can actto seal the volume 55 if the cylinder 23B does not include sidewalls. Inanother embodiment of the invention, the diameter of the bore 57 issubstantially equal to the outer diameter of the rod 24, therebyenabling a friction fit of the cylinder 23B onto the rod 24, whichprevents unwanted lateral movement of the cylinder 23B during a coatingprocess. Accordingly, the rod 24 need not be threaded and lock member 26and nut 25 are not needed.

The interior volume 55 is in communication with the pump 50 via the tube52. The pump 50 supplies gas or fluid to the interior volume 55 causingpressure to increase within the interior volume 55, thereby causing theouter diameter 54 to expand radially outwards from the rod 24, as shownin FIG. 5B. The supplied gas can have a temperature other than roomtemperature. The supplied gas, for example, can have a temperaturebetween 35° C. and 80° C., to induce the evaporation of a solvent,preferably non-volatile solvents. Alternatively, the supplied gas can becooler than 25° C. to retard the evaporation of the solvent, preferableretardation of the evaporation of unlike solvents.

In an embodiment of the invention, the inner diameter 56 is slightlylarger than the diameter of the rod 24 while the outer diameter 54, inan unexpanded state, is less than the inner diameter of the stent 10, aspositioned on the cylinder 23B. In one embodiment, the cylinder 23B hasa length at least equal to the length of the stent 10, thereby enablingmasking the entire length of the inner diameter of the stent 10. Inanother embodiment of the invention, the cylinder 23B is less than thelength of the stent 10, thereby enabling masking of only a portion ofthe length of the inner diameter of the stent 10. The cylinder 23B iscapable of expanding to at least the inner diameter of the stent 10 whenthe pump 50 pumps air into the interior area 55 of the cylinder 23B toincrease the pressure within the cylinder 23B to, for example, 60-80PSI. When the cylinder 23B is in an expanded state, the cylinder 23Bacts to support the stent 10 and to mask the inner surface of the stent10 (as shown in FIG. 5B) during a coating process so that the innersurface of the stent 10 is not coated with the same composition as theouter surface of the stent 10. In another embodiment of the invention,the sidewalls of the stent 10 can also be masked by the cylinder 23B asshown in FIG. 6A.

During operation of the stent mandrel fixture 20B, a stent 10 is loadedonto the fixture 20B by placing the stent 10 over the cylinder 23B whenthe cylinder 23B in an uncompressed state (FIG. 5A). The pump 50 thenpumps gas into the interior area 55 of the cylinder 23B causing theouter diameter 54 of the cylinder 23B to expand radially outwards. Inone embodiment of the invention, the cylinder 23B can expand radiallyoutwards to substantially mask the inner surface of the stent 10, asshown in FIG. 5B. In another embodiment of the invention, the cylinder23B can comprise a flexible and/or thin material, e.g., latex, andexpands radially outwards to substantially mask the inner surface of thestent 10 as well as the sidewalls of the stent 10, as shown in FIG. 6A.

After the cylinder 23B is expanded radially outwards, a spray nozzle(not shown) sprays a composition onto the stent 10. As the innerdiameter of the stent 10 is masked, only the sidewalls and outerdiameter of the stent 10 are coated with a composition. In anotherembodiment of the invention, the sidewalls can also be masked andaccordingly, only the outer surface of the stent 10 is coated with thecomposition.

After the coating of the stent 10, the pump 50 vents gas from within theinterior volume 55, thereby lowering the pressure within the interiorarea 55 and enabling the tube 23B to return to a non-expanded state andfurther enabling removal of the stent 10 from the stent mandrel fixture20B. The stent 10 can then have the inner surface coated viaelectroplating or spray coating.

FIG. 3D illustrates a stent mandrel fixture 20C in accordance withanother embodiment of the invention. The fixture 20C, like the fixture20B, is pneumatic-based. A cylinder 23C, for being placed through a boreof the stent 10, circumscribes a rod 24C. The cylinder 23C is anexpandable tube having an inner volume constrained by the rod 24C. Therod 24C includes an inner bore and outlets 53 in fluid communicationwith the bore that feed gas, from the pump 50, into the interior volumeof the cylinder 23C, thereby causing the cylinder 23C to expand radiallyoutwards. The bore is in communication with a tube 59A, which is incommunication with a coupling 58. The coupling 58 is in communicationwith the pump 50 via a tube 59B. Accordingly, gas from the pump 50 cantravel through the tube 59B to and through the coupling 58 to andthrough the tube 59A to the rod 24C and through the outlets 53 into theinterior volume of the cylinder 23C. The coupling 58 enables the rod 24Cand cylinder 23C to rotate during a coating process without having torotate the pump 50.

During a coating process, the pump 50 pumps air into the cylinder 23Cthereby causing the cylinder 23C to expand to the inner diameter of thestent 10 (when the stent 10 is in an unexpanded state) thereby maskingthe inner diameter. In another embodiment of the invention, the cylinder23C can expand past the inner diameter of the stent 10 to at leastpartially mask the sidewalls of the stent 10. After a coating process iscomplete, the pump 50 can vent gas from the interior region of thecylinder 23C, enabling it to return to its natural uncompressed state.

In an embodiment of the invention, the fixtures 20B and 20C can alsoinclude a pressure monitor disposed within the cylinder 23B or 23C. Thepressure monitor can be coupled to feedback lines that provide the pump50 with a measurement of pressure within the cylinder 23B or 23C so thatthe pump 50 can adjust the amount of gas pumped into the cylinder 23B or23C.

FIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D illustrate a stent mandrelfixture 20D in accordance with another embodiment of the invention. Thefixture 20D comprises a mandrel base 60 for receiving a rod 62; a tubeor cylinder 23D that circumscribes the rod 62 and acts as a maskingelement to mask an inner surface of the stent 10 during a coatingprocess; and a toggle switch 66 that is coupled to the rod 62, whichacts as an expansion causing mechanism. In one embodiment of theinvention, the mandrel base 60 is about 2 inches long with a diameter ofabout ⅜ of an inch and can be made of stainless steel.

The rod 62 has a disk 63 on the distal end. The rod 62 is coupled to thetoggle switch 66 through a bore of the mandrel base 60 such thatactuation of the switch 66 pulls the rod 62 further into the mandrelbase 60, thereby pulling the disk 63 towards the mandrel base 60. Thedisk 63 laterally compresses the cylinder 23D against the mandrel base60, thereby causing it to expand radially outwards. In one embodiment ofthe invention, the rod 62 is about 2.15 inches long with a diameter ofabout 0.28 inches and is made of stainless steel. The disk 63 of the rod62 can also be made of stainless steel and have a diameter of about 0.55inches with a width of 0.3 inches.

The cylinder 23D can be made of or coated with a non-stick material,such as TEFLON or low durometer PEBAX. The cylinder 23D circumscribesand is supported by the rod 62. The cylinder 23D is thereforeconstrained on both ends by the mandrel base 60 and the disk 63.Accordingly, when the cylinder 23D is compressed laterally between themandrel base 60 and the disk 63, as is shown in FIG. 4B and FIG. 5B, thecylinder 23D is forced to expand outwards radially. In an embodiment ofthe invention, the cylinder 23D, in its uncompressed and unexpandedstate, as shown in FIG. 4A and FIG. 5A, has an outer diameter of about0.055 inches and an inner diameter of about 0.030 inches with a lengthof about 1.65 inches.

The toggle switch 66 changes the cylinder 23D between a compressed,expanded state and an uncompressed, non-expanded state. During operationof the stent mandrel fixture 20D, a stent 10 is loaded by placing itover cylinder 23D when the toggle switch 66 is placed in an open stateas shown in FIG. 4A. The toggle switch 66 is then toggled to a closed orcompressed state via an automated control or with human intervention asshown in FIG. 4B. The toggling of the toggle switch 66 pulls the rod 62inwards towards the proximal end of the mandrel base 60, thereby pullingthe disk 63 laterally inwards and compressing the cylinder 23Dlaterally, which causes the cylinder 23D to expand in a radial direction(i.e., the diameter of the cylinder 23D will increase) to mask the innersurface of the stent 10. The stent 10 can then be coated with acomposition and dried while on the cylinder 23D. After application ofthe composition, the toggle switch 66 is moved to an open position,thereby decompressing the cylinder 23D so that the stent 10 can bereleased. As in all embodiments, the stent 10 can then be further driedin an oven until the solvent of the composition is evaporated.

FIGS. 5A and 5B illustrate cross sections of a stent mandrel fixtureaccording to an embodiment of the invention. The stent mandrel fixtureof FIG. 5A and FIG. 5B can include the embodiments shown in FIG. 2A &2B; FIG. 3A-3D; or FIG. 4A-4D. The stent mandrel fixture includes amasking element 23, such as the tube 23A or 23B, the masking element23C, or the cylinder 23D having a bore within. The rod 24, 24C or rod 62travels through the bore, thereby preventing the masking element 23 fromexpanding radially inwards when laterally compressed. When the maskingelement 23 is compressed laterally and expanded radially, as shown inFIG. 5B, the masking element 23 masks the inner surfaces 12C of thestruts 12. Accordingly, during a coating process, only the exteriorsurface 12A and sidewalls 12B of the struts are coated with acomposition leading to a coating 70 (FIG. 5C) on the exterior surface12A and sidewalls 12B. A second coating (not shown) can be applied tothe interior surfaces 12C via spraying, electroplating, or otherconventional coating methods.

FIG. 6A illustrates a cross section of a stent mandrel fixture accordingto another embodiment of the invention. The stent mandrel fixture ofFIG. 6A can include the embodiments shown in FIG. 2A & 2B; FIG. 3A-3D;or FIG. 4A-4D. However, the masking element 23 is capable of partiallyor completely masking the sidewalls 12B in addition to the innersurfaces 12C. Accordingly, only the exterior surfaces 12A will be coatedwith a composition, forming a coating 72 (FIG. 6B), which can, forexample, include a substantially pure drug composition. The maskingelement 23 can then be unexpanded to mask only the inner surfaces 12C asshown in FIG. 5B and a second coating applied, thereby forming coating74 (FIG. 6C), which can include, for example, a substantially purepolymer. In an alternative embodiment, after applying the coating 72,the masking element 23 can be fully unexpanded, as shown in FIG. 5A, andthen a coating applied, thereby encapsulating the coating 72 and allsides of the struts 12 with a coating 76 (FIG. 6D), which can include,for example, a substantially pure polymer. Advantages of the coatingsapplied as in FIGS. 6C and 6D include less coating on the stent 10 asonly the exterior surfaces 12A are coated with a drug; encapsulation ofthe struts 12 prevents delamination or peeling at the edges of thestruts 12; the encapsulating coating 74 or 76 can control drug releaseand have biocompatible properties; and drugs can be placed on the struts12 where needed (e.g., a restenosis drug can placed solely on theexterior surfaces 12A, where it is needed), thereby preventing excessiveuse of the drug.

FIG. 7 illustrates a flowchart of a method 700 of coating a stent usingthe stent mandrel fixture 20A (FIG. 2A-FIG. 2B); 20B (FIG. 3A-FIG. 3D);or 20D (FIG. 4A-FIG. 4D). First, a stent 10 is loaded (710) over amasking element such as the tube 23A, or the cylinder 23B, 23C, or 23D(or other expandable masking element). The masking element is thenexpanded (720) until the masking element has an outer diameter at leastequal to the inner diameter of the stent 10, thereby masking the innersurface of the stent 10. The expansion (720) can be invoked by anexpansion causing mechanism such as the nut 25, the pump 50, or thetoggle switch 66. In an alternative embodiment of the invention, themasking element can be further expanded to completely or partially coverthe sidewalls in addition to the inner surface of the stent 10. Thestent 10 is then coated (730) with a first composition. Due to themasking of at least the inner surface of the stent 10, only the outersurface and possibly the sidewalls (depending on how far the maskingelement is expanded) are coated (730) with the first composition. Themasking element is then returned (740) to an unexpanded state and thestent 10 is removed (750) from the mandrel 24. The stent 10 is thenbaked (760) to remove solvent and so that the composition dries andhardens on the stent 10. The inner surface of the stent 10 is thencoated (770), if desired, with a second composition having a therapeuticsubstance different from a therapeutic substance in the firstcomposition. The coating (770) can be done via spraying orelectroplating the composition. The method 700 then ends.

In another embodiment of the invention, in place of the removing (750)through the coating (770), the masking element can be unexpanded to lessthan the inner diameter of the stent 10 or up to the diameter of thestent 10 and then the stent 10 can be coated with a second composition(e.g., polymer) to encapsulate most or all of the surfaces of the stent10. The stent 10 can then be removed from the masking element and bakedto evaporate any solvent and to harden the coatings.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications can be made without departing from thisinvention in its broader aspects. Therefore, the appended claims are toencompass within their scope all such changes and modifications as fallwithin the true spirit and scope of this invention.

1. A stent mandrel for partially covering a stent during an applicationof a coating composition, comprising: a mask made of or coated with anon-stick material; means for masking the stent so that an outer surfaceof the stent is exposed for coating by a coating substance, the meansfor masking including an inflatable bladder in fluid communication witha pressure source; an engine connected to the mandrel and configured forrotating the stent during the application of the coating composition;and a coupling that decouples rotational motion supplied to the stentfrom the engine from pressure supplied to the bladder from the pressuresource.
 2. The stent mandrel of claim 1, wherein the mask is made from athin material, and wherein the means for masking the stent includesmeans for masking both a luminal surface and a side surface of the stentusing the mask.
 3. The stent mandrel of claim 2, wherein the material ispolytetraflouroethylene.
 4. The stent mandrel of claim 2, wherein thethin material is capable of conforming to the shape of a stent strutwhen radially expanded into the stent strut.
 5. The stent mandrel ofclaim 1, wherein the means for masking the stent includes means formasking a luminal surface of the stent by radially expanding the maskwithout also radially expanding the stent.
 6. A stent support for stentsthat are to be partially coated with a coating composition, comprising:a mandrel base; a masking element; a lever; a rod having a longitudinalaxis and configured to be moved in or out of the base; and means forplacing the masking element on at least a luminal surface of a stentwhen the rod is at least moved parallel to its longitudinal axis and outof the base including a coupling between the rod and the lever, whereinthe coupling converts rotational motion of the lever about an axisperpendicular to the longitudinal axis to motion of the rod parallel tothe longitudinal axis.